Communication systems are designed to reliably transfer information using the underlying physical medium. Well-known communication systems like Ethernet use special wiring (e.g., Cat 5 cable) for exchanging information. Such systems, by design, allow all connected stations to exchange data at a fixed data rate. With the increasing need for ubiquitous exchange of information, a new class of no-new-wire systems has emerged. Such systems use existing infrastructure to exchange information. Power line communication systems are one example of such systems.
Power line communication systems use existing AC wiring to exchange information. Owing to their being designed for much lower frequency transmissions, AC wiring provides varying channel characteristics at the higher frequencies used for data transmission (e.g., depending on the wiring used and the actual layout). To maximize the data rate between various links, stations need to adjust their transmission parameters dynamically in both time and frequency. This process is called channel adaptation. Channel adaptation results in a set of transmission parameters (referred to as tone maps in this document) that can be used on each link. Tone maps include such parameters as the frequencies used, their modulation, and the forward error correction (FEC) used. In high-speed power line communication systems, good channel adaptation is critical to providing high data rates on all links.